[SalesForce] How to include/escape a single quote in field update

That's pretty strange, and seems like a bug since you don't need to do anything in this case to handle single quotes.

It's working for me when I did the following I created a custom label, A_Test, with a value of "haven't", and ran the following and everything worked as expected. Assertions passed and email received with single quote intact. Perhaps you can try this out and see if the assertions fail for you? If they do I'd recommend logging a case with support.

String expected = 'haven\'t';
system.assertEquals(expected, Label.A_Test);
Messaging.SingleEmailMessage email = new Messaging.SingleEmailMessage();
email.setToAddresses(new String[] { 'ralph@example.com' });
email.setSubject('Expected: ' + expected + '. Label: ' + Label.A_Test);
email.setPlainTextBody('Expected: ' + expected + '. Label: ' + Label.A_Test);
system.assertEquals(true, email.getSubject().contains('\''));
system.assertEquals(true, email.getPlainTextBody().contains('\''));
Messaging.sendEmail(new Messaging.SingleEmailMessage[] { email });

For URL encoding, there is EncodingUtil.urlEncode('StringToEncode', 'UTF-8);

The apex String class offers a number of built in escape*() methods. You would typically need to choose the one that matches what you are doing.

For building dynamic SOQL queries you would typically use escapeSingleQuotes. See SOQL Injection.

There is also escapeUnicode().

What are you intending to do with the escaped values?

You may need to combine several of the built in methods to meet your requirements.